THIS INVENTION relates to anti-platelet drugs. In particular, this invention relates to novel diflunisal esters and related compounds having anti-platelet activity, hydroxyl radical scavenging properties, enhanced hepatic clearance and low ulcerogenic potential.
Aspirin (O-acetylsalicylic acid) is well known for treatment of inflammation, fever and pain and is also well established for secondary stroke prevention (The SALT Collaborative Group, 1991, Lancet 338 1345-1349). In regard to the latter, aspirin is known to inhibit the synthesis of thromboxane A2 in platelets by irreversible acetylation of a serine residue close to the active site of cyclooxygenase, an enzyme which catalyses the formation of an unstable endoperoxide intermediate, PGH2, from arachidonic acid (Lecomte et al, 1994, J. Biochem. 269 13207-13215). Thromboxane A2 is a vasoconstrictor and platelet-aggregating agent and is thus potentially thrombotic.
Whilst such an anti-thromboxane A2 effect may be desirable, aspirin also has a destructive effect on the vascular endothelium since it can inhibit synthesis of prostacyclin by a similar mechanism. Prostacyclin, in this regard, is a vasodilator that inhibits platelet aggregation and is thus potentially anti-thrombotic. In the stomach, prostacyclin is one of the important endogenous prostaglandins that provide local cytoprotection, induce gastric mucosal vasodilation, inhibit acid secretion and conserve gastric mucosal integrity (Gaskill et al, 1982, Surgery 92 220-225; Ligumsky et al, 1982, Am. J. Physiol. 242 G337-341; Walus et al, 1980, Proc. Soc. Exp. Biol. Med. 163 228-232). Aspirin therefore has paradoxical effects, being both a beneficial antiplatelet drug and a significant ulcerogen.
It has been proposed that an optimal antithrombotic effect can be achieved by restricting aspirin to the portal circulation where selective inhibition of platelet cyclooxygenase can occur as distinct from the inhibition of vessel wall cyclooxygenase. In other words, this may have the effect of reducing thromboxane A2 production whilst preventing aspirin reaching the post-hepatic systemic circulation where it might also inhibit prostacyclin synthesis and concomitant promotion of thrombotic and/or ulcerogenic injury (Ali et al, 1980, Stroke 11 9-13; Siebert et al, 1983, Clin. Pharmacol. Ther. 33 367-374; Pedersen et al, 1984, N. Engl. J. Med. 311 1206-1211; Roberts et al,. 1986, Lancet 1 1153-1154; McLeod et al, 1988, Austr. NZ. J. Med. 148 207).
Confining the inhibition of cyclooxygenase activity to the portal circulation depends on extensive first pass hepatic de-acetylation of the aspirin, forming platelet-inactive salicylate. Previous studies, however, have demonstrated that the extraction of aspirin by the liver is incomplete: hepatic availabilities being reported to be between 0.6 and 0.8 for man (Harris et al, 1969, J. Pharm. Sci. 58 71-75), sheep (Cossum et al, 1986, J. Pharm. Sci. 75 731-737) and rat (Iwamoto et al, 1982, J. Pharm. Pharmacol. 34 176-180; Wientjes et al, 1988, J. Pharmacol. Exp. Ther. 245 809-815). Thus, substantial quantities of aspirin bypass the liver through an inefficient hepatic extraction and aspirin is not restricted to the portal circulation.
Various aspirin analogues/derivatives have been described in the prior art with improved efficacy in relation to treatment of pain and inflammation. In U.S. Pat. No 5,599,959 (Hosmane et al), there is disclosed analogues of aspirin having the structure: 
wherein R is defined as being selected from the group consisting of hydrogen, methyl, ethyl, n-propyl, l-propyl, n-butyl, l-butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, phenyl, naphthyl and cyclohexyl. R1 is defined as being selected from the group consisting of hydrogen, a C1xe2x80x94C12 alkyl group, F, Cl, Br, I, CO2H, CONHR, CONR2, CO2R, CHO, COR, SO3R, SO2NHR, SC2NR2, OH, OR, OCOR, SH, SR, OCONHR, OCONR2, SCOR, SCONHR, SCONR2 and NH2, NHR, NHCOR and NR2. The foregoing aspirin analogues were shown by Hosmane et al to adsorb into membranes of red blood cell and to decrease membrane viscoelasticity of such cells. According to Hosmane et al, a decrease in membrane stiffness would lead to a decrease in flow resistance experienced by red cells, and hence, a decrease in their mean capillary transit times (mean cell transit time). A positive correlation was also shown to exist between the amount of membrane adsorption and the lipophilicity of the aspirin analogue. Accordingly, Hosmane et al teach that such aspirin analogues may be advantageously used to treat diseases which have origin in poor blood supply or circulation such as heart disease, stroke, painful leg, and calf muscles, chest pain, atherosclerosis and dry gangrene. Hosmane et al, however, neither teach nor suggest compounds having anti-platelet activity with enhanced hepatic clearance and low ulcerogenic, potential.
Diflunisal (2xe2x80x2,4xe2x80x2-difluoro-4-hydroxy-3-biphenylcarboxylic acid) is a salicylic acid derivative and is known to be analogous to aspirin insofar as treatment of inflammation, fever and pain and propensity for gastrointestinal injury. Various diflunisal derivatives have been described in the prior art having enhanced analgesic potency and anti-pyretic activity compared to the parent drug. Related diflunisal compounds are disclosed in U.S. Pat. No 4,044,049 (Ruyle et al). This patent is directed broadly to substituted 5-(phenyl) benzoic acid esters having the general formula: 
wherein X(1-5), R, R1 and R3 are as defined hereinafter. The term R2 is defined in this specification as being selected from the group consisting of hydrogen, lower alkyl (such as methyl, ethyl, butyl pentyl, and the like), lower alkanoyl (where xe2x80x9clowerxe2x80x9d is referring to acetyl, propionyl, butyryl and the like having an upper limit of 4 carbon atoms), and lower alkenyl (such as allyl, butenyl, and the like). In this regard, it should be noted that the only lower alkanoyl ester of 5-(phenyl) benzoic acid exemplified in the specification is 2-acetoxy-5-(4xe2x80x2fluoropheny)-benzoic acid and no other. In particular, this patent is concerned with anti-inflammatory properties of these compounds. However, there is no explicit disclosure in Ruyle et al of O-medium and longer alkyl esters of diflunisal which are the subject of this application nor are there methods disclosed which can result in the production of such esters.
In light of the above, the prior art is deficient in the lack of effective compounds having anti-platelet activity, enhanced hepatic clearance and low ulcerogenic potential.
The current invention arises from the unexpected discovery that by increasing the carbon number in the ester O-acyl moiety of diflunisal and related compounds, a marked enhancement in hepatic extraction results with a simultaneous reduction in ulcerogenicity. This greater rate of hepatic elimination is considered to minimise exposure of these esters to the systemic circulation thereby minimising prostacyclin inhibition within the vessel endothelium. Surprisingly, it has also been found that these and other diflunisal esters have anti-platelet activity as well as hydroxyl radical scavenging properties which make them suitable for use as active agents for treatment and/or control of thrombosis and ischaemic/reperfusion injury of tissues such as liver.
It is therefore an object of the present invention to provide novel diflunisal esters and related compounds having anti-platelet properties and reduced ulcerogenic potential compared to diflunisal and aspirin.
It is another object of the invention to provide pharmaceutical compositions comprising these diflunisal esters as well as methods of treating mammals therewith.
Other objects of the invention will become apparent from the following disclosure.
According to one aspect of the invention, there is provided O-medium alkyl esters of diflunisal and related compounds having the general formula: 
wherein:
n equals 3-13
X is a halogen (chloro, bromo, fluoro and iodo, especially chloro or fluoro), X being on one or more of the phenyl carbon atoms; R is selected from the group consisting of hydrogen, halogen (chloro, bromo, and fluoro), lower alkyl (such as methyl, ethyl, butyl, pentyl and the like), and lower alkoxy (such as methoxy, ethoxy, butoxy, and the like); R1 is selected from the group consisting of hydroxy, amino, loweralkoxy (such as methoxy, ethoxy, butoxy, pentoxy, and the like), lower alkylamino (methylamino, propylamino, pentylamino, and the like), di(lower alkyl)amino (dimethylamino, dibutylamino, propylpentylamino, and the like), diloweralkylaminoloweralkylamino, diloweralkylaminoloweralkoxy, hydroxyloweralkoxy, (3-hydroxypropoxy, 2-hydroxypropoxy, 4-hydroxybutoxy and the like), polyhydroxyloweralkoxy (2,3-dihydroxypropoxy, 2,3,4,5,6-pentahydroxyhexyloxy and the like), loweralkoxyloweralkoxy (ethoxyethoxy), phenyl-loweralkoxy (benzyloxy, phenethoxy and the like), phenoxy, substituted phenoxy (such as loweralkanoylamino, benzyloxy-2-carboxy4-(4xe2x80x2-fluorophenyl), carboxy and carbloweralkoxy, loweralkanoylamino-loweralkoxy, hydrazino, (hydroxylamino), N-morpholino, N-(4-loweralkyl-piperidino) N-[4-(hydroxyloweralkyl)-piperidino], (hydroxyloweralkyl) amino and a naturally occurring amino acid radical with attachment at the N, such as glycine, phenylalanine, proline, methionine - and taurine;
R2 is hydrogen or a halogen or combination thereof; and
R3 is selected from the group consisting of hydrogen, 3-lower alkenyl, 3- and 4-lower alkyl, lower alkoxy, benzyl and halo;
or a pharmaceutically acceptable salt thereof.
Preferably, n=3-5.
Suitably, X is fluoro. In such a case, the fluoro group is preferably on two of said phenyl carbon atoms, more preferably, on the 2xe2x80x2 and 4xe2x80x2 phenyl carbon atoms.
R is preferably hydrogen, halo or lower alkyl.
Suitably, R1 is hydroxy or amino but preferably is hydroxy.
Preferably, R2 is hydrogen.
Preferred representative compounds of the invention include medium and long alkanoyl derivatives of diflunisal and more preferably pentanyl, hexanyl and heptanyl derivatives of diflunisal as well as pharmaceutically acceptable salts thereof.
The term xe2x80x9cpharmaceutically acceptable saltsxe2x80x9d as used herein refers to salts which are toxicologically safe for systemic administration. The pharmaceutically acceptable salts of said benzoic acid may be selected from the group including the alkali (Na, K, Li) and alkali earth (Mg, Ca, Ba), ammonium, aluminium, iron, amine, glucosamine, choline, sulphate, bisulphate, nitrate, citrate, tartrate, bitartrate, phosphate, carbonate, bicarbonate, malate, maleate, napsylate, fumarate, succinate, acetate, terephthalate, pamoate, pectinate and S-methyl methionine salts, piperazine, and the like.
In another aspect, the invention resides in a pharmaceutical composition for treating and/or controlling in a mammal thrombosis, hydroxyl radical-related diseases, inflammation, fever or pain comprising an effective dosage of a compound of Formula I.
Dosage forms of the pharmaceutical composition include tablets, dispersions, suspensions, injections, solutions, syrups, troches, capsules, suppositories, aerosols and the like. These dosage forms may also include injecting or implanting slow releasing devices designed specifically for this purpose or other forms of implants modified to act additionally in this fashion. Slow or controlled release of a compound according to Formula I may be effected by coating the same, for example, with hydrophobic polymers including acrylic resins, waxes, higher aliphatic alcohols, polylactic and polyglycolic acids and certain cellulose derivatives such as hydroxypropylmethyl cellulose. In addition, the controlled release may be effected by using other polymer matrices, liposomes and/or microspheres.
Pharmaceutically-acceptable carriers for systemic administration may also be incorporated into the compositions of this invention.
By xe2x80x9cpharmaceutically-acceptable carrierxe2x80x9d is meant a solid or liquid filler, diluent or encapsulating substance which may be safely used in systemic administration. Depending upon the particular route of administration, a variety of pharmaceutically-acceptable carriers, well known in the art may be used. These carriers may be selected from a group including sugars, starches, cellulose and its derivatives, malt, gelatine, talc, sterotix, pectin, cab-o-sil, acacia, calcium sulfate, stearic acid, magnesium stearate, terra alba, agar, vegetable oils, synthetic oils, polyols, alginic acid, phosphate buffered solutions, emulsifiers, isotonic saline, and pyrogen-free water.
Pharmaceutical compositions of the present invention suitable for oral or parenteral administration may be presented as discrete units such as capsules, sachets or tablets each containing a pre-determined amount of the compound according to Formula I, as a powder or granules or as a solution or a suspension in an aqueous liquid, a non-aqueous liquid, an oil-in-water emulsion or a water-in-oil liquid emulsion. Such compositions may be prepared by any of the methods of pharmacy but all methods include the step of bringing into association the effective dosage of the compound of Formula I with the carrier which constitutes one or more necessary ingredients. In general, the compositions are prepared by uniformly and intimately admixing the compound of Formula I with liquid carriers or finely divided solid carriers or both, and then, if necessary, shaping the product into the desired presentation.
The pharmaceutical composition may be in the form of a sterile injectable preparation, for example as a sterile injectable aqueous or oleaginous suspension. This suspension may be formulated using suitable dispersing or wetting agents and suspending agents which are well known to those of skill in the art.
The active compounds of Formula I and of the compositions of this invention are present in an amount sufficient to treat and/or control thrombosis, hydroxyl radical related diseases such as ischaemic/reperfusion injury of tissue, inflammation, fever or pain. Suitable dosages of the compounds of Formula I and of the pharmaceutical compositions containing such compounds may be readily determined by those of skill in the art. In this regard, the amount of active compounds of Formula I that may be present in the dosage of a pharmaceutical composition according to the invention will vary depending on the host treated, the condition to be treated and/or controlled and the particular mode of administration hereinafter described. For example, a formulation intended for oral administration of humans in need of treatment and/or control of thrombosis may contain the active ingredient, namely, the compounds of Formula I in an amount from 0.2 mg to 5 mg per kg body weight per day (10 mg to 250 mg per patient per day (preferably from about 2 mg to 3 mg per kg body weight per day (100 mg to 150 mg per patient per day). In the case of treatment of inflammation, suitable formulations intended for oral administration of humans may contain the compounds of Formula I in an amount from 0.2 mg to 140 mg per kg body weight per day (10 mg to 7 g per patient per day (preferably from about 0.5 mg to 50 mg per kg body weight per day (25 mg to 3.5 g per patient per day).
It will be understood, however, that the specific dose level for any particular patient will depend upon a variety of factors including the activity of the specific compound employed, the age, body weight, general health, sex, diet, time of administration, route of administration, rate of excretion, drug combination and the severity of the particular disease or condition undergoing therapy.
According to another aspect of the invention there is provided a method for treating and/or controlling thrombosis, hydroxyl radical related diseases, inflammation, pain and fever comprising administering to a mammal in need of such treatment a composition comprising an effective dosage of a compound of Formula I.
Any suitable route of administration may be employed for providing a mammal the composition of the invention. For example, oral, rectal, parenteral, ocular, sublingual, inhalational, buccal, intrathecal, epidural, intravenous, intra-articular, intramuscular, intraperitoneal, sub-cutaneous, transdermal, intravenous, or intracerebroventricular and the like may be employed. It will be appreciated that the particular route of administration will vary, for example, upon the particular disease or condition under therapy.
In yet another aspect of the invention, there is provided a method of treating and/or controlling thrombosis comprising administering to a mammal in need of such treatment a composition comprising an effective dosage of a compound having the general formula: 
wherein:
n equals 0-13
X is a halogen (chloro, bromo, fluoro and iodo, especially chloro or fluoro), X being on one or more of the phenyl carbon atoms;
R is selected from the group consisting of hydrogen, halogen (chloro, bromo, and fluoro), lower alkyl (such as methyl, ethyl, butyl, pentyl and the like), and lower alkoxy (such as methoxy, ethoxy, butoxy, and the like);
R1 is selected from the group consisting of hydroxy, amino, loweralkoxy (such as methoxy, ethoxy, butoxy, pentoxy, and the like), lower alkylamino (methylamino, propylamino, pentylamino, and the like), di(lower alkyl)amino (dimethylamino, dibutylamino, propylpentylamino, and the like), diloweralkylaminoloweralkylamino, diloweralkylaminoloweralkoxy, hydroxyloweralkoxy, (3-hydroxypropoxy, 2-hydroxypropoxy, 4-hydroxybutoxy and the like), polyhydroxyloweralkoxy (2,3-dihydroxypropoxy, 2,3,4,5,6-pentahydroxyhexyloxy and the like), loweralkoxyloweralkoxy (ethoxyethoxy), phenyl-loweralkoxy (benzyloxy, phenethoxy and the like), phenoxy, substituted phenoxy (such as loweralkanoylamino, benzyloxy-2-carboxy-4-(4xe2x80x2-fluorophenyl), carboxy and carbloweralkoxy, loweralkanoylamino-loweralkoxy, hydrazino, (hydroxylamino), N-morpholino, N-(4-loweralkyl-piperidino) N-[4-(hydroxyloweralkyl)-piperidino], (hydroxyloweralkyl) amino and a naturally occurring amino acid radical with attachment at the N, such as glycine, phenylalanine, proline, methionine and taurine;
R2 is hydrogen or a halogen or combination thereof; and
R3 is selected from the group consisting of hydrogen, 3-lower alkenyl, 3- and 4-lower alkyl, lower alkoxy, benzyl and halo;
or a pharmaceutically acceptable salt thereof.
In such a case, n preferably equals 0-6.
Preferred representative compounds which can be used in accordance with the above method include alkanoyl derivatives of diflunisal, more preferably medium and long alkanoyl derivatives inclusive of acetyl, propionyl, butyryl, pentanoyl, hexanoyl and heptanoyl derivatives and pharmaceutically acceptable salts thereof.
In still yet another aspect of the invention, there is provided a method of treating and/or controlling a hydroxyl radical-related disease comprising administering to a mammal in need of such treatment a composition comprising an effective dosage of a compound according to Formula IV.
In such a case, n preferably equals 0-6.
Suitable compounds which can be utilised in the above method include diflunisal as well as alkanoyl derivatives of diflunisal, more preferably medium and, long alkanoyl derivatives inclusive of acetyl, propionyl, butyryl, pentanoyl, hexanoyl and heptanoyl derivatives and pharmaceutically acceptable salts thereof.
In another aspect, the invention resides in a process of preparation of compounds according to Formula I including the step of acylating a compound of general formula: 
with an appropriate acylating agent.
An appropriate acylating agent according to the invention may include a medium alkanoic acid anhydride, particularly a C3xe2x80x94C13 anhydride such as propionic anhydride, butyric anhydride and the like.
According to a further aspect of the invention, there is provided a method of treating and/or controlling thrombosis comprising administering to a mammal in need of such treatment a composition comprising an effective dosage of a compound having the general formula: 
xe2x80x83wherein:
n equals 1-13;
R1 is selected from the group consisting of hydroxy, amino, loweralkoxy (such as methoxy, ethoxy, butoxy, pentoxy, and the like), lower alkylamino (methylamino, propylamino, pentylamino, and the like), di(lower alkyl)amino (dimethylamino, dibutylamino, propylpentylamino, and the like), diloweralkylaminoloweralkylamino, diloweralkylaminoloweralkoxy, hydroxyloweralkoxy, (3-hydroxypropoxy, 2-hydroxypropoxy, 4-hydroxybutoxy and the like), polyhydroxyloweralkoxy (2,3-dihydroxypropoxy, 2,3,4,5,6-pentahydroxyhexyloxy and the like), loweralkoxyloweralkoxy (ethoxyethoxy), phenyl-loweralkoxy (benzyloxy, phenethoxy and the like), phenoxy, substituted phenoxy (such as loweralkanoylamino, benzyloxy-2-carboxy4-(4xe2x80x2-fluorophenyl), carboxy and carbloweralkoxy, loweralkanoylamino-loweralkoxy, hydrazino, (hydroxylamino), N-morpholino, N-(4-loweralkyl-piperidino) N-[4-(hydroxyloweralkyl)-piperidino], (hydroxyloweralkyl) amino and a naturally occurring (amino acid radical with attachment at the N, such as glycine, phenylalanine, proline, methionine and taurine;
R2 is hydrogen or a halogen or combination thereof; and
R3 is selected from the group consisting of hydrogen, 3-lower alkenyl, 3- and 4-lower alkyl, lower alkoxy, benzyl and halo;
or a pharmaceutically acceptable salt thereof.
Preferably, n=1-6
Suitably, R1 is hydroxy or amino but preferably is hydroxy.
Preferably, R2 is hydrogen.
Preferred representative compounds according to Formula III which may be employed advantageously in the above method include alkanoyl salicylic acids inclusive of propionyl, butyryl, pentanoyl, hexanoyl and heptanoyl derivatives as well as pharmaceutically acceptable salts thereof.
In a still further aspect, the invention resides in a method of treating and/or controlling a hydroxyl radical-related disease comprising administering to a mammal in need of such treatment a composition comprising an effective dosage of a compound having a general formula: 
xe2x80x83wherein:
n equals 0-13;
R1 is selected from the group consisting of hydroxy, amino, loweralkoxy (such as methoxy, ethoxy, butoxy, pentoxy, and the like), lower alkylamino (methylamino, propylamino, pentylamino, and the like), di(lower alkyl)amino (dimethylamino, dibutylamino, propylpentylamino, and the like), diloweralkylaminoloweralkylamino , diloweralkylaminoloweralkoxy, hydroxyloweralkoxy, (3-hydroxypropoxy, 2-hydroxypropoxy, 4-hydroxybutoxy and the like), polyhydroxyloweralkoxy (2,3- dihydroxy propoxy, 2,3,4,5,6-pentahydroxyhexyloxy and the like), loweralkoxyloweralkoxy (ethoxyethoxy), phenyl-loweralkoxy (benzyloxy, phenethoxy and the like), phenoxy, substituted phenoxy (such as loweralkanoylamino, benzyloxy-2-carboxy-4-(4xe2x80x2-fluorophenyl), carboxy and carbloweralkoxy, loweralkanoylamino-loweralkoxy, hydrazino, (hydroxylamino), N-morpholino, N-(4-loweralkyl-piperidino) N-[4-(hydroxyloweralkyl)-piperidino], (hydroxyloweralkyl) amino and a naturally occurring amino acid radical with attachment at the N, such as glycine, phenylalanine, proline, methionine and taurine;
R2 is hydrogen or a halogen or combination thereof; and
R3 is selected from the group consisting of hydrogen, 3-lower alkenyl, 3- and 4-lower alkyl, lower alkoxy, benzyl and halo;
or a pharmaceutically acceptable salt thereof.
Preferably, n=1-6
Suitable representative compounds in accordance with Formula III which may be utilised in the above method include but are not limited to alkanoyl salicylic acids inclusive of acetyl, propionyl, butyryl, pentanyl, hexanyl and heptanyl derivatives as well as pharmaceutically acceptable salts thereof.